Photodynamic therapy (PDT) is also called photoradiation therapy, phototherapy, or photochemotherapy. It was first used to treat cancer over 100 years ago. It is treatment that uses drugs, called photosensitizing agents, along with light to kill cancer cells. The drugs only work after they have been activated or “turned on” by certain kinds of light. Depending on the part of the body being treated, the photosensitizing agent is taken orally, injected into the bloodstream or put on the skin. After the drug is absorbed by the cancer cells, light is applied only to the area to be treated. The light causes the drug to react with oxygen, which forms a chemical that kills the cancer cells. PDT may also work by destroying the blood vessels that feed the cancer cells and by alerting the immune system to attack the cancer.
The period of time between when the drug is given and when the light is applied is called the drug-to-light interval. It can be anywhere from a couple of hours to a couple of days and depends on the drug used.
PDT can be used to treat some cancers, or conditions that may develop into a cancer if not treated (precancerous). It is used when the affected area or the cancer is on or near the lining of internal organs. This is usually with cancers or conditions that affect: the skin, the breast, the head, the neck, the mouth, the lung, the gullet (oesophagus), the stomach, the rectum and the bile ducts.
Breast cancer affects one in eight women during their lives. Breast cancer kills more women in the United States than any cancer except lung cancer. No one knows why some women get breast cancer, but there are a number of risk factors. Risks that you cannot change include (a) age; the chance of getting breast cancer rises as a woman gets older; (b) genes; there are two genes, BRCA1 and BRCA2 that greatly increase the risk; women who have family members with breast or ovarian cancer may wish to be tested; (c) personal factors; beginning periods before age 12 or going through menopause after age 55.
Other risks include being overweight, using hormone replacement therapy, taking birth control pills, drinking alcohol, not having children or having a first child after age 35 or having dense breasts.
Symptoms of breast cancer may include a lump in the breast, a change in size or shape of the breast or discharge from a nipple. Breast self-exam and mammography can help find breast cancer early when it is most treatable. Treatment may consist of radiation, lumpectomy, mastectomy, chemotherapy, and hormone therapy.
Breast cancer recurrences after mastectomy pose a therapeutic challenge with few surgical options. If disease is localized, surgical excision can be attempted. However, these lesions often are widespread throughout the chest wall or involve heavily irradiated tissue. Many patients have received aggressive chemotherapy with little to no local response and have exhausted most avenues for local control. Multiple studies show that photodynamic therapy (PDT) provides good tumor kill for primary cutaneous malignancies and suggest its effectiveness in ablating dermal lymphatic recurrences of breast cancer. Food and Drug Administration (FDA) approved uses for PDT include lung and esophageal lesions, but treatment of bladder, head and neck, and other tumor sites with novel approaches has been reported. PDT exploits the accumulation of photosensitizers into the tumor, which then is locally excited with visible light. Selectivity of treatment comes from the excretion of drug from normal tissue over time, promoting a concentration gradient within the tumor plus the location of the activating light. Treatment depth varies with the wavelength of light that activates the sensitizer used. The singlet oxygen that is produced during the transfer of energy from light source to drug disrupts plasma, nuclear, and mitochondrial cell membranes, resulting in apoptosis. Local edema and perivascular stasis occur rapidly, within hours of treatment. Tumor necrosis can be evident within 2 to 24 hours. Photofrin (dihematoporphyrin ether; Axcan Scandipharm, Birmingham, Ala.) is the only FDA-approved photosensitizer available for the treatment of cancer. The light source used to activate Photofrin (630 nm) is topically delivered via lasers by using diffusing catheters and is focused on skin surfaces by using a microlens. This modality has been previously reported in a small number of breast cancer patients with chest wall recurrence, with good responses.
U.S. Pat. No. 6,899,723 ('723) discloses methods and compounds for PDT of a patient's target tissue, using a light source that preferably transmits light to a treatment site transcutaneously. The method provides for administering to the subject a therapeutically effective amount of a targeted substance, which is either a targeted photosensitizing agent, or a photosensitizing agent delivery system, or a targeted prodrug. This targeted substance preferably selectively binds to the target tissue. Light at a wavelength or waveband corresponding to that which is absorbed by the targeted substance is then administered. The light intensity is relatively low, but a high total fluence is employed to ensure the activation of the targeted photosensitizing agent or targeted prodrug product. Transcutaneous PDT is useful in the treatment of specifically selected target tissues, such as vascular endothelial tissue, the abnormal vascular walls of tumors, solid tumors of the head and neck, tumors of the gastrointestinal tract, tumors of the liver, tumors of the breast, tumors of the prostate, tumors of the lung, nonsolid tumors, malignant cells of the hematopoietic and lymphoid tissue and other lesions in the vascular system or bone marrow, and tissue or cells related to autoimmune and inflammatory disease.
In accordance with '723, method of therapeutically treating a target tissue provides destroying or impairing target cell by the specific and selective binding of a photosensitizer agent to the target tissue, cell, or biological component. At least a portion of the target tissue is irradiated with light at a wavelength or waveband within a characteristic absorption waveband of the photosensitizing agent. It is contemplated that an optimal total fluence for the light administered to a patient is determined clinically, using a light dose escalation trial. The total fluence administered externally during a treatment preferably is in the range from 500 Joules to 70,000 Joules.
It should be emphasized that according data published by the US National Cancer Institute, maximal penetration depth achievable for photodynamic therapy is about 1 cm. Practically, depth penetration available for reliable photodynamic therapy can be performed at the penetration depth of 2-3 mm. Providing a photodynamic therapy generating high-energy light fluence characterized by greater depth of radiation penetration into tissues of the patient's body is an unmet and long-felt need.